The present invention relates to a method for detecting the relative location of an image reading head and a light source, and more specifically, to a method for detecting the relative location of the image reading head and the backside light source for a transparent original, wherein both of the image reading head and the backside light source are driven in an image reading system for transparent originals.
The electrical industry has been developed continuously as one of the most important industries in the twentieth century. With the fast progressing in various kinds of computing and processing system, lots of electrical devices including computers, communication devices, and consumer electronics are employed in our daily life. In recent years, the application of image processing apparatus, in combining with the raising processing and storage ability of the computing system or the processors, plays an vital role in image reading, processing, and transferring usage.
Generally, most of the image reading systems can be classified as two categories. The first category is a so-called stationary reading device category. In the first category of image reading systems, the image reading device or image reading head is kept stationary during the document reading process, and the document scanning operation is achieved through moving the originals bypassing the front end of the image reading device or the image reading head. The design is mostly seen on facsimile machines and sheet-feed scanners. The simplified design provides a image reading system with less structural parts and minimize the occupied volume of the whole system.
In contrast to the stationary reading device category, the second category is called as the moving reading device or dynamic reading device category. In the second category of image reading systems, the image reading device or image reading head is driven to move in parallel, or namely in a line-by-line scanning way, in front of the stationary objects which are scanned during the image reading process. The scanning operation is completed by moving the image reading device or image reading head through the whole reading area, such as an original sheet or an object being scanned. The design is generally employed in high-quality scanning systems like typical flat-bed scanning systems, in order to provide raised image quality by the stability in the scanning operation.
In either category of the scanning systems, a line or array of image sensors are provided to read the image with the illumination of a light source. In general, the light source of a fluorescent lamp, a single or more light emitting diodes (LED), or other light emitting device is employed to provide the scanned object with essential illumination and reflect the image on the object to the image sensors.
In the second category of the image scanning systems, or namely the moving reading device image scanning systems, most of the designs are applied for scanning opaque originals. Referring to FIG. 1, for scanning transparent originals 10 such as slides, a backside light source 12 is provided to illuminate the transparent original 10 from the backside. The image reading head 14 is placed in front of the transparent original 10, at the corresponding location of the backside light source 12, in order to read the illuminated image. In a typical flat-bed scanning system, the backside light source 12 is placed in the upper lid and the image reading head 14 is placed under a transparent plate, such as a glass plate, for supporting the originals.
In the illustrated scanning system for scanning transparent originals, both the backside light source 12 and the image reading head 14 are driven to move through the whole original. In the ideal case, the backside light source 12 and the image reading head 14 are aligned exactly in the relative up-down position, and are driven individually but remain in parallel to provide consistent illumination for image reading during the scanning operation.
However, in the real case, the scanner is composed of lots of complicated moving parts. Most of the composing parts, under the mass-production, has some dimension deviation from the designed model. In the fabrication of combining parts, the combination process will also has some unavoidable deviations. The accumulated errors or deviations of parts, fabrication, and even scanning operation might result in the inaccuracy in the alignment of the backside light source 12 and the image reading head 14, or the non-parallel position of the backside light source 12 or the image reading head 14. The mis-alignment in the image-reading or illumination parts causes the problems like image distortion, dark and illuminated regions, and damages the quality of image reading.
In addition, since the backside light source 12 and the image reading head 14 must be driven synchronously during the scanning, some problems may arise from the driving of the backside light source 12 and the image reading head 14. However, the design of conventional scanning systems lacks a systematic approach to determine or measure the alignment between the two devices. The mis-alignment generally causes the non-uniformity in the light-intensity distribution and results in the non-uniformity in the brightness of the scanned image. The severeness of the mis-alignment can only be judged by the scanned image, and the exact relative position or the deviation tolerance of the two devices can hardly be investigated. Namely, no exact data can be granted for design for manufacturing improvements.
The present invention proposes a method for detecting the relative location of an image reading head and a light source, and the method is especially designed for the application in a scanning system for transparent originals. The relative location between an image reading head and a backside light source for illuminating a transparent original can be detected. The design or fabrication error can be measured with accuracy to provide information for improving the quality of image reading and operational characteristics of the scanning system.
The method in the present invention, for detecting the relative location of an image reading head and a light source in an image reading system, includes several steps as follows. At first, the light source is positioned to a first detecting point in a scanning region of the image reading system. The image reading head is moved to pass through the first detecting point while keeping the light source fixed at the first detecting point. At the same time, the scanned images are recorded through the moving process of the image reading head. Finally, the scanned images is processed to provide functional information of the image reading head and the light source.
For acquiring information of the image reading head and the light source at different locations, the same approach can be applied at other points in the scanning region of the image reading system. In the preferred embodiments, a transparent original is placed between the image reading head and the light source in the image reading head moving step and the image recording step.
In the case, the functional information of the image reading head and the light source, such as the oblique of the image reading head, the oblique of the light source, the deviation in aligning the two devices, the usable image reading range of the image reading head, the distance of an aligning point from the boundary of the usable image reading range, the magnifying ratio, the lateral deviation of the image reading head, and the lateral deviation of the light source, can be generated from processing the scanned images.